Daily there are hundreds of thousands of samples of blood drawn in hospitals, medical clinics and doctors"" offices for analytical purposes. Some of this blood is analyzed directly as whole blood without being processed. Some is analyzed after separation of the cellular components of the blood (e.g., leukocytes and erythrocytes) from the fluid portion of the blood (plasma or serum).
For example, whole blood can be used for hematological analysis to measure the total concentration of red blood cells and white blood cells in the whole blood, or to prepare blood smears for microscopic analysis of the different types of cells that are present in the blood. Microscopic analysis can be used to diagnose a number of different diseases that might be present, such as certain types of leukemias or anemias. Very commonly, the patient will have a complete blood count (CBC) performed on a whole blood sample. A CBC typically includes a red blood cell (RBC) count, a white blood cell (WBC) count, a differential white blood cell count to identify the types of white blood cells present, a platelet count and the determination of blood parameters such as total hemoglobin and hematocrit.
Alternatively, whole blood can be processed to separate the cellular components from the fluid portion to obtain serum or plasma. Initially, blood is drawn from a patient into a small glass tube. If the tube contains an anticoagulant, the blood does not coagulate (i.e., form a clot) and the cells remain xe2x80x9csuspendedxe2x80x9d in the plasma. If the tube does not contain an anticoagulant, the blood coagulates. The formation of a clot removes certain protein components from the plasma, with serum remaining as the fluid portion of the blood. Processing whole blood to separate cells from plasma/serum is typically accomplished by centrifugation.
Analysis of other physiological parameters can be performed on the plasma or serum, per se, which contain extracellular components such as proteins, hormones and electrolytes. A patient undergoing a general physical examination will probably have tests performed on both serum and plasma.
Erythrocyte sedimentation rate (ESR) is one of the traditional tests performed on whole blood in hematology laboratories. ESR measures the distance red blood cells sediment, or fall, in a vertical tube over a given period of time. The measurement of sedimentation is calculated as millimeters of sedimentation per hour and takes greater than one hour to complete. The principle behind ESR is that various xe2x80x9cacute phasexe2x80x9d inflammatory proteins can affect the behavior of red blood cells in a fluid medium (e.g., decrease the negative charge of RBCs). Inflammatory proteins, such as fibrinogen, will typically appear in the blood, or increase in concentration, during inflammatory processes, such as arthritis. The result is decreased negative charge (zeta-potential) of the erythrocytes that tends to keep them apart, and a more rapid fall of the cells in the analysis tube. The greater the fall of red blood cells in the vertical tube measured at a given period of time, the higher the ESR. A high (i.e., elevated) ESR is indicative of the presence of inflammatory proteins, (i.e., an active inflammatory processes, such as rheumatoid arthritis, chronic infections, collagen disease and neoplastic disease).
The process of collecting the blood specimen and the particular anticoagulant used are crucial in determining an accurate ESR. For example, in one well-known technique known as the Westergren method, blood is collected in the presence of the anticoagulant, sodium citrate, whereas in the modified Westergren procedure, EDTA is used as the anticoagulant. The modified Westergren procedure has become the standard for measuring ESR because it allows the ESR to be performed from the same tube of blood as is used for hematologic studies. Essentially, ESR is a test that has been practiced for decades without much change in the procedure.
Hematocrit (HCT) or packed red blood cell volume is the ratio of the volume of red blood cells (expressed as percentage or as a decimal fraction) to the volume of whole blood of which the red blood cells are a component. In the micromethod for determining hematocrit, tubes containing whole blood are centrifuged for 5 min at 10-12000 g to separate the whole blood into red cells and plasma. The hematocrit is calculated from the length of the blood column, including the plasma, and the red cell column alone, measured with a millimeter rule. One of the problems with this technique is that it""s time consuming and erroneous results may occur as a result of incorrect reading of the levels of cells and plasma or if a significant concentration of plasma becomes trapped within the red cell layer.
It is an object of this invention to measure both erythrocyte sedimentation rate and hematocrit simultaneously with the centrifugation of the whole blood specimen, which is performed for other purposes. In other words, the object is to obtain two critically important blood parameters during the routine centrifugation that is almost universally performed on every blood sample drawn for analytical purposes, without additional manipulation or handling of the blood sample.
Another object is to perform these determinations as rapidly as possible, and have results available much faster than with currently practiced methods.
The invention resides in a method of calculating the erythrocyte sedimentation rate and hematocrit simultaneously with the centrifugation of whole blood for other purposes and apparatus for performing the method.
A sample of whole blood is collected in a container in the presence or absence of an anticoagulant. With the dimensions of the container known, the volume is ascertainable by the blood""s level in the container. Thus, the blood level relative to a fixed point in the container need only be measured. A sample is centrifuged to create an interface between the erythrocytes and the plasma or serum. The location of the interface relative to a fixed point in the container is measured as well as the elapsed time between initiating the centrifugation of the blood and the time the interface between the erythrocytes and the plasma or serum is formed. The time and dimensional factors are measured optically and permanently recorded. The erythrocyte sedimentation rate of the sample is calculated from the elapsed time and the hematocrit of the sample is calculated from the difference between the two measured locations.
The step of measuring the location of the original sample, the interface and the elapsed time of forming the interface is performed by a video camera which records on tape and which is monitored by a video monitor.
A chart comparing the results of measuring erythrocyte sedimentation rate by standard known techniques and that obtained by the above-described method was made to show the correlation of the two techniques. Thereafter, the chart may be referred to in order to obtain erythrocyte sedimentation rate expressed in millimeters per hour (conventional manner) from a measurement of the elapsed time (expressed in seconds) for interface formation.
The above and other features of the invention including various and novel details of construction and combination of parts will now be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the particular method and apparatus for determining erythrocyte sedimentation rate and hematocrit embodying the invention is shown by way of illustration only and not as a limitation of the invention. The principles and features of this invention may be employed in varied and numerous embodiments without departing from the scope of the invention.